Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
I agree that a counterpoise would benefit by a connection through an RF
choke to safety ground, to establish a path for fault currents.
I have two separate RF grounds that I connect together when running my
coil. In the front of my garage is a simple 8 foot copper clad ground
rod, with 6 inches above the ground.
About 10 feet away from that ground rod, on the side of the garage, we
had an addition built, so I buried a horizontal 8-foot length of 3/4"
copper pipe on top of the concrete foundation footing, about 5 feet
deep, with a vertical 3/4" copper pipe up to the surface, in contact
with the foundation wall.
Our breaker panel is grounded to the water pipe entering the house, plus
an independent ground rod.
If I try to read the resistance between either of my buried RF grounds
to the mains ground, I get a reading of over 4 Meg Ohms. If I try to
read the resistance between the two RF grounds (about 10 feet apart), my
DMM reads open circuit! I live in Eastern Massachusetts, and the soil
about my house is rocky fill and well drained, but by no means a desert.
It's not at all clear what benefit such a high impedance connection has
to 60 Hz concerns.
I think my RF grounds are fairly reasonably constructed by most
standards, but I have no faith that they would safely ground a fault
condition. So this brings me to my point (thank you for reading so
far!) - How to construct an RF choke between the RF and green-wire
grounds that can support a fault current and still isolate RF from the
mains ground? Trouble is, I'm unaware of any actual measurements of the
magnitude of the RF transients that appear on our RF grounds.
Regards, Gary Lau
MA, USA
> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
>
> At 12:49 PM 10/9/2006, you wrote:
> >Original poster: Mddeming@xxxxxxx
> >In a message dated 10/9/06 1:27:38 P.M. Eastern Daylight Time,
> >tesla@xxxxxxxxxx writes:
> >Original poster: John <guipenguin@xxxxxxxxx>
> >
> >If I cant drive a grounding rod for RF ground, what is this counter
> >pose under the coil I hear people mention?
> >
> >Thanks,
> >
> > John.
> >
> >Hi John,
> >
> > A counterpoise is a type of "virtual ground". consisting of
> > foil, wire mesh (chicken wire etc.) or radial wires arranged in a
> > daisy wheel at least as long and broad as the coil is high or the
> > topload diameter, whichever is greater. This is placed underneath
> > the unit with RF ground end of secondary attached to it. The
> > topload "sees this as ground and all works. A foil one is cheapest
> > and easiest, but wastes somewhat more power in eddy currents.
> > Radial wires are the most efficient, but hardest to do and keep
> > straight. a large square or circle of wire mesh is a good
> > compromise. NOTE: During operation, the counterpoise is floating at
> > unknown high potential with respect to earth ground. DO NOT
TOUCH!!!!!
>
>
> For the latter reason, the counterpoise SHOULD be connected to the
> "green wire" safety ground. I'd use a RF Choke of some sort, just to
> keep RF off the building safety ground.